This project is concerned with the biochemical and genetic characterization of a number of metabolite transport systems in Escherichia coli, with emphasis on the structural relationships of the component proteins. Several transport systems are under primary investigation to take advantage of the unique features they exhibit. The transport of vitamin B12 is associated with a receptor protein in the outer membrane of the cell, and the relation of this receptor to the subsequent steps of transport is of prime interest. Evidence exists that the receptor can exist on the outer membrane in a functionally inactive state. Methionine transport allows study of the uptake of the two separate methionine isomers and also of the regulation of uptake activity by a form of feedback control by the internal methionine pool. This study of regulation of transport activity is being extended to other amino acid transport systems. Finally, specialized transducing phages carrying the genes for membrane proteins are being constructed to aid in the identification and isolation of specific membrane proteins, with the initial systems being those for the lactose permease and the vitamin B12 receptor. Bibliographic references: Kadner, R. J. 1975. Regulation of methionine transport activity in Escherichia cili. J. Bacteriol. 122: 110-119. Kadner, R. J., and H. H. Winkler. 1975. Energy coupling for methionine transport in Escherichia coli. J. Bacteriol. 123: 985-991.